1. Field of the Invention
The present invention relates to a semiconductor memory device. The present invention relates more particularly to a semiconductor memory device using a system wherein, before data are overwritten, all data stored in a block containing the sector to be overwritten are deleted.
2. Description of the Related Art
Non-volatile semiconductor memory devices include devices using a system wherein data are overwritten by deleting previously stored data, then writing new data. Flash memory is an example of this type of memory device. Flash memory uses FAT (Floating gate Avalanche injection Transistors) as storage elements. In FAT, for example, the state where charge accumulates in the floating gate is defined as xe2x80x9c0xe2x80x9d and the state where charge does not accumulate in the floating gate is defined as xe2x80x9c1.xe2x80x9d When defined in this way, it is possible to overwrite a xe2x80x9c0xe2x80x9d when xe2x80x9c1xe2x80x9d is stored in the storage element, but not to overwrite a xe2x80x9c1xe2x80x9d when xe2x80x9c0xe2x80x9d is stored. Consequently, data are written after the stored data are deleted in semiconductor memory devices using this type of storage element.
Also, these semiconductor memory devices include devices using a control system wherein the storage region is divided into a plurality of blocks and each block is divided into a plurality of sectors. One block comprises 16 sectors, for example. A memory device with this system writes and reads data in units of sectors, but deletes data in units of blocks.
When both these systems are employed, the memory device must delete an entire block of data, even when writing only one sector of data. In this write operation, data stored in other sectors of that block are transferred once to buffer memory and stored there temporarily. After the data of that block are deleted, these stored data are rewritten to the original block along with the one sector of new data.
Because data are deleted in units of blocks, these semiconductor devices have the advantage that data deletion can be controlled with small scale circuitry, but the disadvantage of requiring a large capacity buffer memory.
It is an object of the present invention to provide a semiconductor memory device that deletes data in units of blocks, but does not require a large capacity buffer memory.
For this reason, the semiconductor memory device relating to the present invention comprises: memory means divided into a plurality of blocks, each comprising a plurality of sectors, for storing user data in units of sectors; control means for writing the user data to a sector of an unused block and copying the user data stored in not-rewriting sector of the used block to the other sectors of the unused block, when rewriting user data stored in the sector of the used block.
When rewriting data, a semiconductor memory device relating to the present invention selects a new storage block from an unused block and writes data to a sector of this new storage block. Consequently, a buffer for temporarily handling data which are not to be overwritten is not necessary. Data in other sectors are copied to the new storage block from the old storage block.